Improvement in a piston for a refrigeration compressor

ABSTRACT

The piston (P) comprises a tubular skirt ( 10 ), and a head (H) affixed in the interior of the skirt ( 10 ), close to an end edge ( 11 ) of the latter and carrying a suction valve ( 20 ). The head (H) comprises a central hub ( 30 ) having an end front face ( 30   a ) and incorporating radial wings ( 31 ) whose end edges ( 31   a ) are affixed to the skirt ( 10 ). The central hub ( 30 ) defines, with the skirt ( 10 ) and the radial wings ( 31 ), respective suction axial passages ( 32 ). The head (H) further comprises a cover ( 40 ) having a contour concentric to the inner contour of the skirt ( 10 ) and having a front face ( 40   a ) and a rear face ( 40   b ) which is affixed to the central hub ( 30 ) by the end front face ( 30   a ) of the latter, the contour of the cover ( 40 ) maintaining, with the inner contour of the skirt ( 10 ), a radial gap which defines a suction annular opening ( 42 ) to be closed by the suction valve ( 20 ).

FIELD OF THE INVENTION

The present invention refers to an improvement introduced in a piston of the type used in a compressor of refrigeration systems and which presents a head portion incorporated in the interior of one of the ends of a tubular cylindrical skirt portion, to be axially displaced inside a compression chamber in a cylinder of a cylinder crankcase of the compressor.

BACKGROUND OF THE INVENTION

In a reciprocating compressor, driven by a linear motor, the operations of gas suction and compression are carried out by reciprocating axial movements of the piston in the interior of a cylinder closed by a head and, in some constructions, assembled inside a hermetic housing of the compressor. The piston is driven by a motor unit of the compressor.

Pistons for refrigeration compressors usually present a monolithic construction, defining, in a single piece, the formation of a head portion and of a skirt portion, such piston construction being obtained, for example, by means of machining from a metal stock, usually steel. This production process is expensive and presents a high material waste.

There are also known other processes of obtaining pistons in a single piece, for refrigeration compressors, such as cold forming, stamping, etc. However, such processes not only have a high cost of production, but also produce parts having a high level of dimensional uncertainties, affecting the actuation of the piston in the compressor.

These drawbacks are even greater in the constructions in which the suction is provided through the body of the piston.

Besides the drawbacks above, the monolithic constructions for refrigeration pistons do not allow constructing pistons which present, besides a minimum cost of material and production, the possibility of simultaneously providing a piston which is light but with no loss of its qualities of resistance, low porosity, low friction coefficient, etc., which are mainly relevant in long pistons and, more particularly, in pistons which operate in a compressor of the type which does not present oil lubrication, or also in a compressor having gas bearings.

Patent document PCT2008/000192 (WO2009/003260), of the same assignee, presents a piston construction of the type comprising a cylindrical tubular skirt which is closed by a head formed in a separate piece and affixed, preferably by interference, in the interior of the skirt, close to an end edge of the latter.

In this prior construction, the piston is formed in two different parts defined by the skirt and by the head, the latter being provided with a front face, usually coplanar to a plane containing the end edge of the skirt, and also with suction openings selectively closed by a suction valve carried by the head of the piston.

The head is formed by a central hub, usually tubular and cylindrical, incorporating radial wings whose end edges are affixed against the skirt, in the interior of the latter. Thus, the contour of the central hub remains radially spaced from the skirt, defining respective suction openings between the radial wings, the front face of the head being defined by the front end face of the central hub.

In a particular construction of said prior art, the piston head further comprises a cylindrical peripheral ring, incorporated, in a single piece, to the end edges of the radial wings and seated and affixed, preferably by interference, in the interior of the skirt.

In said prior solution, the piston head is built in a single piece, defining not only the structural portion for fixation to the skirt, but also, through the front face thereof, the support surface for the suction valve and which should present a suitable and non-excessive radial gap in relation to the inner contour of said end edge of the skirt.

Although the prior solution is constructively and operationally advantageous in relation to older constructions, in which the skirt and the head are formed in a single piece, it still presents the drawback of demanding more complex and costly productive processes in order to reduce the limitations in shape caused by the formation of the head in a single piece. The complexity, cost and shape limitations mentioned above are even more significant when the head further incorporates, in a single piece, the peripheral ring to be seated and affixed against the skirt. In such case, the shape limitations and the complexity of the productive processes tend to produce an annular gap having excessive radial dimensions between the central hub and the peripheral ring of the head, demanding the use of suction valves of greater thickness and mass to minimize the risk of fatigue, due to the flexion degree to which the suction valves are subjected in said annular gap, mainly in the cases in which there is a high pressure difference between the suction and the discharge of the compressor.

Besides the drawbacks above, the piston head construction in a single piece does not allow its formation in different materials.

OBJECTIVE OF THE INVENTION

It is thus an objective of the present invention to provide an improvement in the type of piston considered herein, in order to allow the easy manufacture thereof, at a relatively reduced cost, having less limitation on the shape and employing less material for forming the piston head.

Another objective of the present invention is to provide an improvement in a piston, such as mentioned above, which allows constructing long pistons from different materials, not only between the skirt and the head, but also in the formation of the latter, using different manufacturing processes, said materials being defined as a function of the demands of each specific part of the piston during its operation in the compressor.

A further objective is to provide a piston which allows, in an easy and reliable manner, the suction to be obtained through the interior of the piston itself.

SUMMARY OF THE INVENTION

These and other objectives are achieved through an improvement in a piston for a refrigeration compressor, said piston comprising a tubular skirt, usually cylindrical, and a head affixed in the interior of the skirt, close to an end edge of the latter and carrying a suction valve.

According to the improvement of the present invention, the piston head is formed: by a central hub, of reduced contour in relation to that of the skirt, having an end front face and incorporating, in a single piece, radial wings whose end edges are affixed to the skirt, in the interior of the latter, said central hub defining, between the contour thereof and the skirt and between the radial wings, respective suction axial passages; and by a cover defined by a plate having a contour concentric to the inner contour of the skirt, and having a front face and a rear face which is affixed to the central hub, by the end front face of the latter, the contour of the cover maintaining, with the inner contour of the skirt, a radial gap which defines a suction annular opening to be selectively closed by the suction valve.

The present improved constructive solution uses a skirt formed by a tube extension and a piston head formed in two pieces defined by the central hub and by the cover, which pieces, due to the fact of being separate and presenting less complex configurations, may be produced of different materials and through relatively simpler and cheaper processes than those necessary to produce a head in a single piece, particularly in the configurations in which the central hub has the end edges of the radial wings thereof incorporating, in a single piece, a peripheral ring circumferential extension to be radially seated and affixed against the skirt, in the interior of the latter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below, with reference to the enclosed drawings, in which:

FIG. 1 represents, schematically, an exploded perspective and partially cut view of a first piston construction for a refrigeration compressor and which presents, in separate pieces, a tubular skirt, a central hub, a cover, a suction valve and a screw for affixing the valve;

FIG. 2 represents, schematically, a front top view of the piston construction illustrated in FIG. 1, however in the assembled condition and without the suction valve;

FIG. 3 represents, schematically, a cross-sectional view of the piston illustrated in FIGS. 1 and 2, said cut being taken according to line in FIG. 2, however also illustrating the suction valve in the operative and inoperative positions thereof;

FIG. 4 represents, schematically, an exploded perspective and partially cut view of a second piston construction for a refrigeration compressor and which presents, in separate pieces, a tubular skirt, a central hub carrying a peripheral ring, a cover, a suction valve and a screw for affixing the valve;

FIG. 5 represents, schematically, a front top view of the piston construction illustrated in FIG. 4, however in the assembled condition and without the suction valve;

FIG. 6 represents, schematically, a cross-sectional view of the piston illustrated in FIGS. 4 and 5, said cut being taken according to line VI-VI in FIG. 5, however also illustrating the suction valve in the operative and inoperative positions thereof;

FIGS. 7, 8 and 9 represent, respectively, a perspective view of a constructive alternative of the massive central hub, a perspective view of a cover to be adapted to the central hub, and a diametric cross-sectional view of the cover-central hub set in the assembled condition;

FIGS. 10 and 11 represent a diametric cross-sectional view of a cover-central hub set in the assembled condition, built according to two other constructive alternatives; and

FIGS. 12, 13 and 14 respectively represent a perspective view of another constructive alternative of a central hub provided with a through hole, a perspective view of a cover to be adapted to the central hub, and a diametric cross-sectional view of the cover and central hub set in the assembled condition.

DESCRIPTION OF THE INVENTION

The present invention will be described below for a piston of the type used for pumping refrigerant gas in a refrigeration compressor.

Refrigeration compressors usually comprise a cylinder having an end closed by a valve plate (both not illustrated) and defining, with the cylinder, a compression chamber. The cylinder further presents an opposite end, through which is assembled the piston, which reciprocates in the interior of the cylinder during the suction and compression cycles of the refrigerant fluid in the operation of the compressor, said movement being obtained by the operation of a motor unit (not illustrated), operatively coupled to said piston.

In some compressor constructions, such as those illustrated and described below, the suction of the refrigerant fluid occurs through the piston, in which is mounted the suction valve. For these constructions in which the suction occurs through the piston, a head of the latter, described below, presents at least one suction opening, selectively closed by a respective suction valve carried by the head of the piston.

The present invention provides a construction for a piston P, in which the latter comprises a usually cylindrical tubular skirt 1 which is closed, next to an end edge 11, by a head H, formed in a separate piece from the skirt 10 and being affixed in the interior of the latter, next to said end edge 11 by a suitable securing means, such as gluing, welding, mechanical interference, etc. The head H carries at least one suction valve 20 illustrated in FIGS. 1 and 3.

The skirt 10 is defined by a respective steel tube extension, preferably having an outer hardening surface treatment, and presents an inner end region 10 a, adjacent to the end edge 11 and which is configured to affix the head H, whose peripheral contour is internal to an axial projection of the outer contour of the skirt 10.

According to the invention, the head H is formed by a central hub 30, usually obtained from a metal alloy suitable for the work conditions of the piston and already known in the art, said central hub 30 presenting a reduced contour in relation to that of the skirt 10, having an end front face 30 a and incorporating, in a single piece, radial wings 31 whose end edges 31 a are affixed in the skirt 10, in the interior of the inner end region 10 a thereof. The central hub defines, between its contour and the skirt 10 and between the radial wings 31, respective suction axial passages 32.

The head H is also formed by a cover 40 defined by a plate, also in a metal alloy which is equal or different from that used for forming the central hub 30, and usually presenting a circular contour, concentric to the inner contour of the skirt 10 and having a front face 40 a and a rear face 40 b which is affixed to the central hub 30, by the end front face 30 a of the latter, with the contour of the cover 40 maintaining, with the inner contour of the skirt 10, a radial gap R defining a suction annular opening 42, maintained in fluid communication with the suction axial passages 32 and to be selectively closed by the suction valve 20.

As it may be observed in the drawings, the suction annular opening 42 is kept axially spaced from the suction axial passages 32, allowing that upstream of the first a plenum is formed to accumulate refrigerant gas to be supplied to the suction annular opening 42, whenever occurs the opening of the suction valve 20. This constructive arrangement minimizes load losses in the feeding of refrigerant gas to the interior of the compression chamber.

The assembly of the head H in the interior of the skirt 10 is carried out so that the front face 40 a of the cover 40 is coplanar to a plane containing the end edge 11 of the skirt 10. This constructive arrangement allows the suction valve 20, usually in the form of an annular blade having a median diametric portion for fixation, to be simultaneously seated against the front face 40 a of the cover 40 and against the end edge 11 of the skirt 10, when in its non-operative condition of closing the suction annular opening 42. Usually, the suction valve 20 is affixed to the head H, by means of a central screw 25, passing through the diametric median portion of the suction valve 20 and threaded in a respective threaded hole 41 provided in the cover 40.

In the embodiment illustrated in FIGS. 1 to 3, the end edge 31 a of each radial wing 31 is fitted and affixed in a recess 12 provided in the interior of the skirt 10, in the inner end region 10 a of the latter, and open to the end edge 11 thereof. The recess 12 may occupy only a circumferential extension of the inner contour of the skirt 10, sufficient to receive a respective radial wing 31, said recess 12 defining a respective step, in relation to said inner contour, axially spaced back in relation to said end edge 11 of the skirt 10. However, as illustrated, it is usually provided a single recess 12, which is continuous and occupies the entire inner circumferential contour of the skirt 10.

It should be understood that the fixation of the central hub 30 in the interior of the skirt 10 may be carried out without the need for providing the recess 12.

Due to the fact that the parts of skirt 10, central hub 30 and cover 40 are separate from each other, each of said parts may be obtained from a specific process and from a material more suitable to the function to be exerted by each of said parts.

It should be further understood that the present solution also foresees the possibility of using the same process for obtaining said parts which comprise the piston in the present invention, as well as the same material for obtaining said parts, such characteristics not to be taken as limiting the present solution.

It should be understood that the cover 40 may be affixed to the central hub 30 by different suitable means, such as by welding, gluing, mechanical interference with or without threading.

According to the constructive forms illustrated in FIGS. 4 to 14, the end edges 31 a of the radial wings 31 incorporate, in a single piece, a peripheral ring circumferential extension 35 to be radially seated and affixed against the skirt 10, in the interior of the latter.

As previously mentioned in relation to FIGS. 1 to 3, the peripheral ring circumferential extension 35 is preferably fitted and affixed in a recess 12, provided in the interior of the skirt 10 in the region of the end edge 11 of the latter, open to said end edge 11 of the skirt 10 and occupying a respective circumferential extension of the inner contour of the skirt 10, in order to define an annular step, in relation to said inner contour, axially spaced back in relation to said end edge 11 of the skirt 10.

Thus, although not illustrated herein, it should be understood that each radial wing 31 may have the end edge 31 a thereof incorporating a peripheral ring circumferential extension 35 which extends, to both sides of said radial wing 31, by opposite circumferential extensions which are kept spaced from the other peripheral ring circumferential extensions of 35 incorporated to each one of the other radial wings 31.

In the constructions which incorporate peripheral ring circumferential extensions 35, the suction axial passages are defined between the central hub 30 and the peripheral ring circumferential extension or extensions 35. In the constructions illustrated in FIGS. 4 to 14, the end edges 31 a of the radial wings 31 are joined by a single peripheral ring circumferential extension 35.

Due to the fact that the parts of skirt 10, central hub 30 and cover 40 are separate from each other, they may present simpler production shapes, which is particularly advantageous in the cases in which the central hub 30 incorporates one peripheral ring circumferential extension 35.

The construction of the central hub 30 in a separate piece from the cover 40 allows obtaining, without negative consequences to the productive processes and to the shape simplicity of the central hub 30, an annular gap having suitable radial dimensions between the cover 40 and the skirt 10 and, consequently, using suction valves 50 of reduced thickness and lower mass, without the risk of breaking from fatigue caused by the level of flexion to which they are subjected in said annular gap, especially in the cases in which a high pressure difference exists between the suction and discharge of the compressor.

Independently of providing one or multiple peripheral ring circumferential extensions 35, they present an axial height equal to that of the radial wings 31, said peripheral ring circumferential extension 35 being coplanar to the radial wings 31.

As it may be observed, regardless of the constructive alternative applied to the subject piston P, the radial wings 31 are formed in order to remain axially spaced back and spaced away from the rear face 40 b of the cover 40, allowing for the already mentioned axial spacing between the suction axial passages 32, formed between the central hub 30 and the skirt 10, and the suction annular opening 42, formed between the cover 40 and the skirt 10.

In FIGS. 1 to 11, the axial spacing between the cover 40 and the radial wings 31 is obtained by providing the latter axially spaced back and away from the end front face 30 a of the central hub 30.

According to the illustrations in FIGS. 1 to 6, the central hub 30 presents an axial through hole 33 open to the end front face 30 a thereof, and the cover 40 incorporates, in the rear face 40 b thereof, a central axial pin 43 which is fitted and affixed in the axial through hole 33 of the central hub 30, when seating the rear face 40 b of the cover 40 against the end front face 30 a of the central hub 30, to secure the cover 40 to the central hub 30.

The central hub provided with a through hole is advantageous in the case of connecting the piston to the connecting rod, which in turn is connected to the motor. This through hole may be used to glue the connecting rod. The advantage of the concept of fitting by hole and pin is the concentricity obtained in the assembly of the two components, making easier the joining process (brazing or gluing).

As illustrated in FIGS. 7 to 9, the central hub 30 may be massive and incorporate, in the end front face 30 a thereof, a central axial pin 34, the cover 40 being provided with a central axial hole 44 open to the rear face 40 b of the latter and optionally also to the front face 40 a thereof, in which is fitted and affixed the central axial pin 34 upon seating the rear face 40 b of the cover 40 against the end front face 30 a of the central hub 30, for fixing the cover 40 to the central hub 30.

As in the previous embodiment, this construction also facilitates the assembly and to obtain concentricity. In relation to the process of obtaining the components, in the case of a sintered central hub, it is easier to obtain it without the through hole. The cover with the hole could be provided by a simple stamping process, which would bring cost benefits.

In this construction, after mounting the piston, a thread is machined in the top, as illustrated in FIG. 6. In this machining, the pin of the hub may be eliminated, the through hole remaining in its place. The elimination of the pin does not affect the whole, since said pin is provided to facilitate the mounting and joining process. After the parts are brazed or glued, the pin may be machined for forming the thread for the suction valve screw.

Specifically in the construction of FIG. 10, the cover 40 is provided with a central axial hole 44 of a relatively large diameter, open to the rear face 40 b of said cover 40, the central hub 30 being massive and having the end portion 36 thereof projecting axially beyond the radial wings 31, to be fitted and affixed in the central axial hole 44 of the cover 40.

In this embodiment, the joining region in which would be the glue or the weld (from the brazing) is flat, thus exposing the glue or weld to traction tensions. However, glues are more resistant to shearing forces, which is achieved with the hub defining its own fitting. The production of the hub by sintering may become easier if the pin is not present.

In the construction being described, the suction valve 20 is affixed to the head H of the piston P, as already described, that is, by providing a threaded hole machined after the assembly.

FIG. 11 illustrates a constructive form for the head H, in which the cover 40 has the rear face 40 b thereof seated and affixed, by weld or glue, against the end front face 30 a of the central hub 30.

In this construction, in which the fitting guide/pin between the cover and the central hub has been eliminated, the cover may be manufactured in a simpler manner, reducing cost. However, the assembly may be somewhat impaired due to the lack of a way to centralize said cover in relation to the central hub.

As previously described, the suction valve 20 is affixed to the head H of the piston P, by providing a threaded hole machined after the assembly.

In the embodiment illustrated in FIGS. 12 to 14, the radial wings 31 have the same axial height of the central hub 30 and are coplanar thereto. In this case, the central hub 30 presents an axial through hole 33 having a larger diameter and open to its end front face 30 a. The cover 40 incorporates, in the rear face 40 b thereof, a central axial pin 43 comprising a base portion 43 a having a larger contour than that of said axial through hole 33 and an assembly portion 43 b, having a smaller contour and which is fitted and affixed in the axial through hole 33 of the central hub 30, upon the seating of said base portion 43 a against the end front face 30 a of the central hub 30, to affix the cover 40 thereto. In this construction, the axial height of the base portion 43 a of the central axial pin 43 defines the axial spacing between the suction axial passages 32 and the suction annular opening 42.

This construction has the advantage of allowing the cover with the fitting pin to be produced by cold forming instead of stamping. This process, which first uses a wire, results in less material waste than the stamping process. Furthermore, the manufacturing of the hub would be simpler through a sintering process, since the piece presents only one height, as opposed to the hub with a fitting pin, for example, which presents several heights in the same part.

As described above, the suction valve 20 is affixed to the head H of the piston P, by providing a threaded hole machined after the assembly.

It should be further observed that the constructive alternatives described herein may be presented individually as particular constructions, or also partially or totally combined to each other. 

1. An improvement in a piston for a refrigeration compressor, said piston comprising a tubular skirt, and a head affixed in the interior of the skirt, close to an end edge of the latter and carrying a suction valve, the improvement being characterized in that the head is formed: by a central hub having a contour reduced in relation to that of the skirt, having an end front face and incorporating, in a single piece, radial wings whose end edges are affixed to the skirt, in the interior of the latter, said central hub defining, between its contour and the skirt and between the radial wings, respective suction axial passages; and by a cover defined by a plate having a contour concentric to the inner contour of the skirt, and having a front face and a rear face which is affixed to the central hub by the end front face of the latter, the contour of the cover maintaining, with the inner contour of the skirt, a radial gap which defines a suction annular opening to be selectively closed by the suction valve.
 2. The improvement, according to claim 1, characterized in that the front face of the cover is coplanar to a plane containing said end edge of the skirt.
 3. The improvement, according to claim 1, characterized in that the end edge of each radial wing is fitted and affixed in a recess provided in the interior of the skirt in the inner end region of the latter and opened to the end edge thereof.
 4. The improvement, according to claim 3, characterized in that the recess occupies a circumferential extension of the inner contour of the skirt, defining a respective step, in relation to said inner contour, axially spaced back in relation to said end edge of the skirt.
 5. The improvement, according to claim 4, characterized in that it comprises a continuous single recess occupying the inner circumferential contour of the skirt.
 6. The improvement, according to claim 1, characterized in that the end edges of the radial wings incorporate, in a single piece, a peripheral ring circumferential extension which is radially seated and affixed against the skirt, in the interior of the latter.
 7. The improvement, according to claim 6, characterized in that the peripheral ring circumferential extension is fitted and affixed in a recess, provided in the interior of the skirt in the region of the end edge of the latter, open to said end edge of the skirt and occupying a respective circumferential extension of the inner contour of the skirt, in order to define an annular step, in relation to said inner contour, axially spaced back in relation to said end edge of the skirt.
 8. The improvement, according to claim 7, characterized in that the end edges of the radial wings are joined by a single peripheral ring circumferential extension.
 9. The improvement, according to claim 7, characterized in that the peripheral ring circumferential extension presents an axial height equal to that of the radial wings, said peripheral ring circumferential extension being coplanar to the radial wings.
 10. The improvement, according to claim 1, characterized in that the radial wings are axially spaced back and away from the rear face of the cover.
 11. The improvement, according to claim 10, characterized in that the radial wings are axially spaced back and away from the end front face of the central hub.
 12. The improvement, according to claim 11, characterized in that the central hub presents an axial through hole open to the end front face thereof, the cover incorporating, in the rear face thereof, a central axial pin which is fitted and affixed in the axial through hole of the central hub, upon the seating of the rear face of the cover against the end front face of the central hub, to secure the cover to the central hub.
 13. The improvement, according to claim 11, characterized in that the central hub is massive and incorporates, in the end front face thereof, a central axial pin, the cover being provided with a central axial hole open to the rear face of the latter and in which is fitted and affixed the central axial pin upon the seating of the rear face of the cover against the end front face of the central hub, to secure the cover to the central hub.
 14. The improvement, according to claim 10, characterized in that the radial wings have the same axial extension of the central hub and are coplanar thereto.
 15. The improvement, according to claim 14, characterized in that the central hub presents an axial through hole open to the end front face thereof, the cover incorporating, in the rear face thereof, a central axial pin comprising a base portion having a greater contour than that of said axial through hole and a mounting portion, having a smaller contour and which is fitted and affixed in the axial through hole of the central hub, upon the seating of said base portion against the end front face of the central hub, for securing the cover to the central hub.
 16. The improvement, according to claim 14, characterized in that the cover is provided with a central axial hole open to the rear face of the latter, the central hub being massive and having an end portion projecting axially beyond the radial wings, to be fitted and affixed in the central axial hole of the cover. 